Luteolytic Role of Prolactin During the Estrous Cycle of the Rat

Abstract

To determine the luteolytic role of prolactin on corpora lutes during the estrous cycle of the rat and the effect of ergocornine (EC) on this mechanism normally cycling rats treated with ergocornine-methanesulfonate a prolactin release inhibitor were injected with ovine prolactin and ovarian weight and corpora lutea (CL) were studied. 26 rats were injected intraperitoneally with 50 mcg EC/100 gmbodyweight for 4 days at proestrus and 14 of these rats received 1 subcutaneous injection of 1 mg prolactin. The EC administration during 1 cycle with or without prolactin resulted in a significant increase in ovarian weight (p less than .001). The number of CL per ovary was significantly greater in the rats treated with EC alone than in the controls or in rats treated with both EC and prolactin (p less than .001). In the second experiment 24 rats received the EC doses for 3 cycles and during each cycle on the first day of estrus 11 of the rats received 1 mg prolactin. EC again significantly increased bodyweight (p less than .001) but this effect was completely prevented in the prolactin-treated rats. Though EC administration increased the number of CL in the ovaries concomitant prolactin administration again reduced the number of CL to normal. It is concluded that the normal rise in blood prolactin on the day of proestrus and continuing into estrus serves to induce luteolysis of the previous crop of CL formed during each cycle.